Method and apparatus for reading and verifying holograms

ABSTRACT

A system and method for reading the information stored in holograms and other diffractive objects. The information is read by analyzing the diffraction pattern produced when a laser beam is focused onto a small spot on the object and scanned across the object.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is related to the inventor's U.S. patentapplication entitled QUANTUM DOT SECURITY DEVICE AND METHOD, filed Dec.31, 1998 (Attorney Docket No. 640002.506). the disclosure of which isincorporated herein by reference.

TECHNICAL FIELD

This invention relates to holography, and, more particularly, to ahologram reader/verifier.

BACKGROUND OF THE INVENTION

Prior art hologram readers have depended on the use of holograms havinga special format or special characteristics. Examples of prior arthologram readers are illustrated in FIGS. 1 a and 1 b. In the hologramreader of FIG. 1 a, a holographic bar code is illuminated by a laserbeam 520 that is generated by a laser 525. A pattern of spots 505 isthen reconstructed onto a set of photodetectors 500 positionedspecifically to detect spots at particular positions.

In the hologram reader of FIG. 1 b, a hologram 510 containing anon-focused image recording is illuminated by a laser beam 520 that isgenerated by a laser 525. The laser beam 520 is incident at itsreference (or conjugate reference) angle to reconstruct an image 555onto a ground glass screen 550. where it can be seen by a human observer560.

Another type of prior art hologram reader (not shown) does not actuallyread a hologram but instead compares a wavefront recorded in a hologramto a reference wavefront. Yet another type of prior art hologram reader(not shown) simply compares a single 2-D view of the hologram to astored 2-D reference image.

-   -   U.S. Pat. No. 4,641,017 to Lopata, entitled Fraud Resistant        Credit Card System    -   U.S. Pat. No. 5,331,443 to Stanisci, entitled Laser Engraved        Verification Hologram And Associated Methods    -   U.S. Pat. No. 4,761,543 to Hayden et al., entitled, Holographic        Security Devices And Systems    -   U.S. Pat. No. 4,108,367 to Hannan, entitled Token And Reader For        Vending Machines    -   U.S. Pat. No. 5,712,731 to Drinkwater et al., entitled Security        Device For Security Documents Such As Bank Notes And Credit        Cards    -   U.S. Pat. No. 5,306,899 to Marom, et al., entitled        Authentication System For An Item Having A Holographic Display        Using A Holographic Record    -   U.S. Pat. No. 4,131,337 to Moraw, et al., entitled Comparison        Reader For Holographic Identification Cards    -   U.S. Pat. No. 3,905,019 to Aoki, et al., entitled Pattern        Recognizing Optical Apparatus    -   U.S. Pat. No. 5,666,417 to Liang, et al., entitled Fluorescence        Authentication Reader With Coaxial Optics    -   U.S. Pat. No. 5,465,243 to Boardman, et al., entitled Optical        Recorder And Reader Of Data On Light Sensitive Media    -   U.S. Pat. No. RE 035,117 to Rando, et al., entitled Scanner With        Coupon Validation

The prior art hologram readers described above and in the above-listedpatents are capable of reading holograms only if the holograms arespecially adapted for the reader. There is therefore a need for ahologram reader that is capable of reading all kinds of hologramswithout the need for the holograms to be specially adapted for thereader and is capable of reading variable information from holograms.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is a schematic drawing showing a prior art hologram reader.

FIG. 1 b is a schematic drawing showing another prior art hologramreader.

FIG. 2 a is a schematic drawing of a diffraction pattern typical of arainbow hologram illuminated at a point using a perpendicular beam.

FIG. 2 b is a schematic drawing of a diffraction pattern typical of acomplex hologram containing both diffraction grating components andrainbow hologram components.

FIG. 3 is a schematic drawing of one embodiment of a hologram reader inaccordance with the present invention.

FIG. 4 is a schematic illustration of a typical fluorescent quantum dotincluding a core and a cap of organic molecules.

FIG. 5 is a schematic drawing of two representative labels containing ahologram, a fluorescent material, and encrypted data in the form of acharacter string printed directly onto the labels.

FIG. 6 is a schematic illustration of a credit card verifier, includingthe hologram reader of FIG. 3, a magnetic stripe reader, and anelectronics subsystem.

FIG. 7 is a schematic drawing of the type of pattern formed when half ofthe diffraction pattern from a single point complex hologram is recordedin an image, half of the diffraction pattern from the next single pointalong a line in the hologram is recorded slightly offset from the firston the same medium, and so on for a series of points along a line acrossthe hologram.

FIG. 8 is a flow chart of a system for using hologram readers and labelprinters to detect and track counterfeit products.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 2 a illustrates the diffraction pattern typically obtained from areflective “rainbow” hologram 300 when an illumination beam (not shown)is incident perpendicular to the surface of the hologram 300. Theillumination beam incident at an angle corresponding to a reference beam(not shown) angle used to make the hologram 300 will produce afirst-order diffracted beam that forms a straight line segment insteadof an arc. Inside a first-order arc as shown in FIG. 2 a are “blobs” 310of light that relate to the features of the image that would be visiblethrough an illuminated point on the hologram 300. In order to read arainbow hologram, it is only necessary to identify and track these.blobs 310 as the point of illumination is moved to all salient points onthe hologram 300. For example, the salient points on a hologram can bedefined as those points on a line through the hologram 300, parallel toan edge of a card or label the hologram is on, and a predetermineddistance from the edge.

FIG. 2 b illustrates a diffraction pattern 320 obtained from a combinedrainbow hologram and diffraction grating image. Small spots 350. 360,370 formed on the pattern correspond to regions containing diffractiongratings, while lines or arcs 315 correspond to regions containingrainbow hologram components or “2D” hologram components. If the lines orarcs 315 contain blobs 310, the corresponding hologram component isusually a 3D hologram. If the lines or arcs 315 contain only asubstantially featureless or uniform distribution of light, thecorresponding hologram component is a “2D” hologram.

While standard image processing techniques can be used to identify thesize, shape and location of each blob 310, it is helpful to takeadvantage of properties specific to holograms in order to simplify thefeature detection and identification task. Unless holograms are blazed,they produce diffraction patterns that are approximately radiallysymmetric, as are the spots 360 shown in FIG. 2 b. However, if theholograms are blazed, the positions of the +1 and −1 orders aresymmetrical but the brightness of one is substantially higher than thatof the other, as are the spots 370 shown in FIG. 2 b.

For a hologram reader to be able to distinguish between differentholograms, certain features of the holograms are important. Thesefeatures include spot location, blob location, blob asymmetry, blobsize, blob shape, blob velocity, blob envelope, and stray light, each ofwhich are discussed below.

The location of a blob can usually be defined as the location of itsbrightness peak. Alternatively, blob location can be defined as centerof mass of the intensity distribution. Radial coordinates areappropriate, since the overall pattern will have a large degree ofradial symmetry.

Blob asymmetry can be defined as the ratio of intensities ofcorresponding blobs in the +1 and −1 orders. Each blob pair will haveits own asymmetry.

Blob size can be defined as the maximum width of the region covered by ablob. Coverage in turn can be defined as having an intensity greaterthan some threshold level determined by the peak intensity of the bloband the background brightness.

In most diffraction patterns from holograms used commercially today,blobs are either point-like or line-like. Line-like blobs occur on thearcs shown in FIG. 2, while point-like blobs occur anywhere in thediffraction pattern. The hologram diffraction pattern shown in FIG. 2 bhas both kinds of blobs. Other blob shapes are possible, and the imageprocessing software should have the capability of detecting the presenceof unusual shapes.

As a hologram is being read by a point of illumination moving across thehologram, the blobs in the diffraction pattern move and change in apiecewise continuous fashion. Blob velocity is the rate-of-change of theblob's location, asymmetry, size and shape in the diffraction patternwith respect to change of location of the illuminated point on thehologram.

In a rainbow hologram, the arc (as seen in FIGS. 2 a and 2 b) is definedby the limits of the blob boundaries as they move in response tochanging location of the illuminated point. The blobs never move outsidethe boundaries of the arc. The arc itself corresponds to the size andshape of an H-1 hologram used to make the rainbow hologram, or of anaperture through which H-1 light was transmitted on its way to formingan H-2 hologram. The position, curvature and orientation of the arc,then, provide information about the physical apparatus used to make thehologram.

In most holograms, there is stray light in the diffraction pattern. Thislight forms dim symmetric patterns upon illumination with anormal-incidence beam, but it has no apparent connection with thevisible image. Ordinarily these stray diffraction components result fromscattered light in the hologram recording apparatus in which thescattered light is recorded as a hologram along with the object light. Acommon technique of holographers is to illuminate a hologram with laserlight and look through it to see an image of the apparatus that was usedto record the hologram.

All information recorded in a hologram is extractable via thediffraction pattern produced (e.g., FIGS. 2 a and 2 b) by theillumination of each point of the hologram. Ordinarily, holograms usedin document security are mass-produced from a single original masterhologram, and the diffraction patterns are the same for all of theholograms. However, new low-cost hologram recording materials andinexpensive lasers have been developed that have begun to make itpractical to produce large numbers of one-off holograms, each containingunique information. In order to read the information in such holograms,it is either necessary to design the holograms to be easy to read (as inthe prior art), or to design a reader, such as a reader according to apreferred embodiment of the present invention, that is capable ofreading all diffraction patterns produced by points of the hologram.

FIG. 3 illustrates a hologram reader in accordance with one embodimentof the present invention. The hologram reader includes a laser diode600, focusing optics 630, preferably with aberration correction, a firstbeamsplitter 605, a color-selective filter 662, an image sensor 620, atime-gated line array sensor 625, spectrum-forming optics 615, 635, anda second beamsplitter 605. The laser diode 600, preferably having theshortest wavelength available, generates a beam 650 that is shaped bythe focusing optics 630 to form a converging spherical wave. Theconverging spherical wave converges to a small spot on a hologram 690,which is hot-stamped onto a credit card 680. A suitable laser diode 600that may be used as the light source for the hologram reader is a greenfrequency-doubled laser diode. However, blue laser diodes or UV laserdiodes may be preferred as they become commercially available atreasonable cost.

The hologram 690 on the card 680 may be transparent, in which case arelief surface of the hologram 690 is preferably coated with ahigh-refractive index material (not shown) so that the hologram 690 issignificantly bright. Suitable high-refractive index materials includetitanium oxide or zinc sulfide. If the hologram 690 is transparent, thesurface of the card 680 underneath the hologram 690 may be provided withfeatures detectable through the hologram, such as patterns offluorescent ink, colored ink, fibers, magnetic inks, or opticallyvariable inks.

In operation, the laser beam 650 diffracts from the hologram 690 to forma pattern on the image sensor 620. The image sensor 620 does not sensethe entire image in the hologram. Instead, the image sensor 620 sensesthe pattern of diffracted light from one illuminated spot on thehologram 690. The color-selective filter 662 ensures that the imagesensor 620 receives only light of the same color as the illuminatinglaser beam 650, and therefore receives predominantly diffracted,scattered and reflected light. If the illuminating laser beam 650 isdirected at an appropriate angle to the hologram 690, corresponding tothe angle between reference and object beams (not shown) used inmanufacturing the hologram 690, only positive diffracted orders willfall onto the image sensor 620 placed directly above the hologram.Alternatively, the illuminating laser beam 650 may be directedperpendicularly to the hologram 690, as indicated in FIG. 3, therebyenabling the image sensor 620 to receive both positive and negativediffracted orders while placed directly above the hologram 690.

Illumination of fluorescent inks printed on the substrate of the card680 induces the emission of fluorescent light. This fluorescent lightpasses through the spectrum-forming optics 615, 635 to the secondbeamsplitter 605, which directs the fluorescent light onto thetime-gated line array sensor 625. The time-gated line array sensor 625images the spectrum of the fluorescent light. A stop 692 blocks thedirect reflection (zero-order diffracted beam) of the illumination laserbeam 650 from striking the line array sensor 625.

Fluorescence from different substances has two primary distinguishingfeatures: emission spectrum and temporal behavior. For example, manyorganic dyes have a very short fluorescence lifetime so that if they areilluminated with a picosecond pulse of excitation light, they emit abrief pulse of fluorescence shorter than a nanosecond. Other fluorescentsubstances emit fluorescence for hundreds of nanoseconds followingexcitation. Many materials are fluorescent to some degree, but most haveshort fluorescence lifetimes; so it is advantageous to use a fluorescentink with a long fluorescence lifetime, thereby providing the opportunityto exclude background fluorescence by time-gating methods.

In the embodiment illustrated in FIG. 3, the line array sensor 625 istime-gated and the laser diode 600 is pulsed. If the fluorescencelifetime of the fluorophores in the printing on the substrate of thecard 680 is longer than typical fluorescence lifetimes of ordinarymaterials, then by selectively detecting only fluorescent light receivedmore than, say, 100 nanoseconds following the excitation pulse,background fluorescence is effectively excluded.

One example of a suitable fluorescent material is formed using quantumdots 210, as illustrated in FIG. 4. The quantum dots 210 are preferablycomposed of CdSe and coated with a cap 220 of ZnSe. Such ZnSe-cappedCdSe quantum dots are known to have fluorescence lifetimes on the orderof 100 nanoseconds. Alternatively, the line array sensor 625 can simplyhave a response time on the order of tens or hundreds of nanoseconds,and the laser diode 600 can be modulated at a rate of one to tens ofmegahertz. The fluorescence lifetime can then be measured as a functionof the phase difference between the illumination modulation and thefluorescence signal. In any case, the line array sensor 625 detects thefluorescence spectrum of any ink or other fluorescing substance underthe hologram 690 at the illuminated spot.

Examples of labels 400, 410 formed by holograms 450 having an underlyingfluorescent material 430 are illustrated in FIG. 5. In both cases, thehologram 450 is semi-transparent hot stamping foil applied over asubstrate 460, which may be formed by paper. The fluorescent material430 is preferably printed directly on the substrate 460. The hologram450 has a void in which encrypted data in the form of a character string470 is printed directly onto the substrate 460. The labels 400, 410preferably have an adhesive backing (not shown) and a peel-offprotective silicone paper back (not shown):

The fluorescent substance 430 may be a fluorescent ink containingfluorophores. It is advantageous to use a patterned fluorescentsubstance 430 on the substrate 460 having a distinctive fluorescencespectrum. A suitable fluorescent substance 430 is a fluorescent inkcontaining fluorophores, such as the ZnS-capped CdSe quantum dots 420described above. The quantum dots 420 are preferably of specific sizesso that the fluorescence spectra will be relatively narrow. Specificorganic dyes such as Rhodamine 6G, which has a distinctive peakfluorescence wavelength, may be used. The fluorescent substance 430 isdescribed in greater detail in co-pending patent application entitledQUANTUM DOT SECURITY DEVICE AND METHOD, filed concurrently herewith, andwhich is incorporated herein by reference.

The credit card 120 of FIG. 5 is representative of the full class oflabels, tags, documents, identification cards, authentication labels,paper currencies, seals, and other items on which a hologram,diffractive image, security label or other security device may beplaced. The holograms 690, 450, 140 shown in FIGS. 3, 5 and 6,respectively, are representative of the full class of diffractive imagesincluding dot-matrix holograms, 2D3D holograms, stereograms, kinegrams,kineforms, Bragg holograms, embossed holograms, holograms embossed intocolored film, holographic hot stamping foils, pixelgrams, electron-beamdiffractive patterns, and binary optical patterns. As used herein, theterm “substrate” means any surface or substance on which a hologram isplaced or held in close proximity to, including any inks, fibers,embossing, chemical treating, magnetic properties, or other propertiesor features of the surface or substance.

Returning to FIG. 3, the image sensor 620, in addition to sensing thepattern of light diffracted by the hologram 690 or 450, also detectslight scattered from the substrate of the card 680 or 460 due to fibers,texture, or other properties of the substrate material. Light diffractedby a hologram 690, 450 typically produces a much higher contrast patternthan light scattered uniformly by, for example, a white substrate.Holograms, however, typically produce distinctive diffraction patternsthat can be subtracted from the sensed pattern. Changes in the averageintensity of light received by the image sensor 620, with the diffractedpatterns subtracted out, correspond to changes in the amount ofdiffusely scattered light from the substrate due to printed patterns orother light-affecting patterns on the substrate. Thus, the hologramreader shown in FIG. 3 can read holograms, fluorescent patterns, andlight scattering or light absorbing patterns, as long as such patternsare evident in light of the wavelength range emitted by the laser diode600. Although a laser diode 600 is used as the illumination source forthe hologram reader of FIG. 3, it will be understood that other lightsources may be used, such as any well-collimated (spatially coherent)white light source. In such cases, the diffractive patterns, spots andscattered light will usually be discernible by the image sensor 620.

Components, modules and combinations of components in the optical andelectronic subsystems of the reader may be substituted for otherequivalent components, modules, and combinations of components may besubstituted, with the objectives of sensing the diffracted light patternfrom the illuminated spot on the hologram and/or the amount of scatteredlight from each point on or under the hologram, and/or the amount,timing or spectrum of fluorescence emitted from the hologram or itssubstrate.

Wavelength-selective filters (not shown) may be inserted in the opticalpath from the hologram 690 to the image sensor 620 and/or in the opticalpath from the hologram 690 to the time-gated line array sensor 625. Thewavelength-selective filters limit detected light to a desired range ofwavelengths. For example, since scattered light and diffracted light areof the same wavelength as the laser diode 650, a filter that istransmissive to the wavelength of the laser diode 650 but reflective orabsorptive to other wavelengths may be advantageously inserted betweenthe sensor 620 and beamsplitter 610. Similarly, a filter that isreflective or absorptive to light at the wavelength of the laser diode650 and transmissive to light in the fluorescence bandwidth of thefluorophores may be inserted between the sensor 625 and beamsplitter605.

Alternatively, the beamsplitter 610 may be a polarizing beamsplitter anda quarter-wave plate 608 may be inserted between the beamsplitter 610and the hologram 690 such that laser light is transmitted nearly 100% atthe beamsplitter on its way to the hologram 690, and is also nearly 100%reflected on its way to the image sensor 620. In this case, thebeamsplitter 610 may be a wavelength-selective polarizing beamsplitterso that most of the fluorescence light is directed to the line arraydetector 625, as indicated in FIG. 6.

The hologram reader shown in FIG. 3 may be combined with readers usingother technologies. For example, a reader/verifier using multipletechnologies is shown in FIG. 6 for use in detecting counterfeit creditcards. In addition to including an optical read head 110, which may bethe hologram reader of FIG. 3, the reader/verifier of FIG. 6 includes aconventional magnetic stripe reader 130. The optical read head 110 readsa hologram 140 on a credit card 120, while the magnetic stripe reader130 reads information recorded on a conventional magnetic stripe (notshown) on the credit card 120 while the credit card 120 slides through aslot 150. The reader/verifier also includes an electronics subsystem100. The electronics subsystem 100 preferably includes a microprocessor(not shown), a field programmable gate array (“FPGA”) (not shown) and aread only memory (“ROM”) (not shown), which contains software that isexecuted by the microprocessor. The electronics subsystem 100 alsopreferably includes means for communicating with external systems suchas a computer (not shown) or telephone network (not shown).

The FPGA in the electronics subsystem 100 is provided to do the imageprocessing. An alternative implementation uses an Artificial NeuralNetwork (ANN). In fact, any image processing means capable ofrecognizing salient features of a diffraction pattern may be used todistinguish between the diffraction patterns of different holograms andof counterfeit and valid holograms or other diffractiveanti-counterfeiting devices known variously as DOVIDs, holograms,stereograms, kineforms, dot-matrix holograms, kinegrams, pixelgrams andso on.

A suitable FPGA that can be used in the electronics subsystem is a model6216 FPGA available from Xilinx. The FPGA can be programmed to performalmost any desired signal-processing function. For example, the FPGA maybe programmed by downloading a configuration file to the FPGA. Theconfiguration file determines the pattern of interconnections among thelogic gates on the FPGA. In the case of the Xilinx 6216 FPGA, the FPGAhas 128 pins available for input and output, and there are approximately35,000 logic gates on the FPGA. All of the logic gates can be operatedin parallel, synchronously or asynchronously. There are also designtools commercially available for designing the configuration file forthe FPGA. A preferred approach in some applications, however, employsevolutionary computation methods to design configuration files. Thisevolutionary computing approach is within the skills of an individual orteam of individuals having ordinary skill in genetic algorithms orgenetic programming, FPGA structure and design methods. chip-levelelectronics and the mathematics of image processing. Alternatively,evolutionary design tools for FPGA configuration files are commerciallyavailable from New Light Industries, Ltd., of Spokane, Wash. 99224 underthe trade name of “FPGA-Generator”™.

In the preferred embodiment of the invention, an evolutionary techniqueis used to design FPGA-based algorithms in the electronics subsystem forfeature recognition and extraction. In one version, the following stepsare carried out:

-   -   1. A target function is defined by visually identifying features        in a set of diffraction patterns to produce feature-tagged        images.    -   2. A trial function is defined by specifying a matrix to serve        as a convolution template.    -   3. A population of templates is generated randomly, and each        member of the population is used to produce a set of convolved        images of a training set of images    -   4. The convolved images produced by each member of the        population are compared to the target set of feature-tagged        images to produce a fitness value for the member, such that the        fitness represents the degree of correspondence between the        produced convolved images and the feature-tagged images.    -   5. Using standard genetic algorithm techniques, the templates        are recombined and/or mutated depending on their fitness to        evolve an optimum template.

The precise choice of recombination and mutation operators, and theother GA parameters such as recombination rate, mutation rate and size,population size, elitism, etc., can affect the speed at which evolutionproceeds. At this time, there is not a known best choice of operatorsand GA parameters for all classes of problems.

In operation, the reader/verifier of FIG. 6 detects counterfeit creditcards 120 by reading the hologram 140. More specifically, a series ofpoints across the hologram 140 are illuminated as explained above withreference to FIG. 3 as the credit card 120 is drawn through the slot150. Diffraction patterns from the points are formed on the image sensor620 where they are converted to video signals. The video signals areanalyzed by the electronics subsystem 100 to extract a feature vectorcorresponding to the values of the significant features of thediffraction patterns in the hologram 140. The feature vector is thencompared to a database of feature vectors from valid and invalidholograms, and the hologram 140 is classified according to thesimilarity of its feature vector to vectors in the database. Dataidentifying the feature vectors for a valid hologram may also possiblybe stored on the magnetic stripe and read by the magnetic stripe reader130 for comparison with the feature vectors for the hologram 140.

The electronics subsystem 100 may also build a representation of thescattering and fluorescence information extracted from the credit card120 to determine validity or invalidity of the credit card 120. Theoptical read head 110 used in the hologram reader of FIG. 6 is thuscapable of sensing diffractive properties, fluorescence properties,light scattering properties and light absorptive properties at a pointon the credit card 120. If the imaging sensor and/or the line arraysensor or the associated electronics are appropriately designed, thereader/verifier can also sense differences between those properties frompoint-to-point.

A preferred way to build a representation of the diffraction informationin the hologram 140 is to detect intensity peaks in the diffractionpattern and generate a list of the locations, sharpness and relativebrightness of the peaks. When a series of diffraction patterns areobserved at a series of regions across the item, it is advantageous torepresent the diffractive properties of the entire item either as alist-of-lists or as a compiled, sorted list.

A simple way to represent the diffraction information is to halve thediffraction pattern and save only the position and intensity dataobtained from that portion. A representative image of a complete set ofdiffraction patterns from a line across a hologram is then constructedby stacking the data, as illustrated in FIG. 7. A plurality of blobs820, 830, 840 then trace paths across the resulting composite image, andany spots 800, 850, 860 from diffraction grating components also tracepaths across the resulting composite image. This representative imagemay then be tested by convolving it with a similarly obtainedrepresentative image of each of one or more reference images, which maycorrespond for example to valid and counterfeit holograms. The paths dueto blob and spot motion obtained as in FIG. 7 are substantiallyinvariant with respect to the particular choice of hologram points thatare sampled, as long as the scale is essentially unchanged.

As mentioned above, an advantage of the hologram reader illustrated inFIG. 3 is that it can read virtually any type of hologram. Thus avariety of techniques can be used to record holograms that are usablewith the hologram reader of FIG. 3. Each of these hologram has its ownparticular set of characteristics. Some of the characteristics orparameters useful for classifying different kinds of holograms anddiffractive images include:

-   -   1. recording medium;    -   2. reference and object beam angles and positions;    -   3. dot size, shape, spacing, placement, grating angle, and        grating period in dot-matrix holograms;    -   4. rainbow (Benton), classical, 2D3D, stereogram, or dot matrix        holograms;    -   5. transmissive or reflective:    -   6. reflectivity-enhancing layers;    -   7. color selectivity of recording medium and Bragg grating        structure;    -   8. color properties of the recording and reconstruction        geometry;    -   9. encoded reference beam or object beam; and    -   10. features and characteristics of a substrate on which the        hologram is laminated or hot-stamped.

The hologram reader of FIG. 3 may be integrated into a comprehensiveanticounterfeit/security system, as illustrated in FIG. 8. Theanticounterfeit/security includes one or more sites 700 formanufacturing anticounterfeit/security labels bearing detectable randomdata on substrates covered by transparent holograms, one or moremanufacturing sites 710, 705 for products, one or more hologram readersat each manufacturing site, label printers at each manufacturing site,one or more intermediate distribution points 730, 720 with hologramreaders, one or more distribution endpoints 750, 760 with hologramreaders, and a computer network consisting of a hierarchy of nodes 740,750, 720.

The random data (e.g., in the labels 400, 410 shown in FIG. 5, thelocations of fluorescent dots 420 under the holograms 450) are read atthe label manufacturing sites 700 and stored in a database. Eachhologram printer at the manufacturing sites 700 has associated with itan encryption engine. The encryption engine combines a representation ofthe random data corresponding to the dots 420 on the labels 400, 410with private key information securely hidden inside the encryptionengine and variable information generated inside the encryption engineto produce an encrypted character string 470 (FIG. 5), which is thenprinted on the labels 400, 410 by the label printer.

The printed labels are placed on products, which are distributed viaintermediate and final distribution points. The labels may be read atthe distribution points by hologram readers that are associated withdecryption engines. The hologram readers read the random data from thesubstrates underneath the holograms and use the random data as a publickey to decrypt the character string printed on the label, withoutdetermining the private key securely hidden in the encryption engine. Ifa label has been counterfeited or illegitimately produced, either thecharacter string will not be decryptable or the random data will not becontained in the label manufacturer's database.

The term, “character string” is used here inclusively of any encodedinformation, including bar codes, optically readable alphanumericcharacters, encoded magnetic stripes, magnetically readable alphanumericcharacters, optically readable bit strings, icons, and the like.

Information relating to the particular labels passing through eachdistribution point and their validity or invalidity is collected by anetwork of computer nodes and analyzed at one or more sites. A centralcomputer node may download information to the distribution sites toalert them to particular counterfeiting threats or to upgrade theirdecryption engines and/or download upgrades to encryption engines to thelabel printers.

The anticounterfeit/security system illustrated in FIG. 8 is capable ofdetecting counterfeit products at any point in the manufacturing anddistribution flow, and can also collect and analyze product flow. Ifcounterfeits are detected, the temporal and geographic pattern of theirappearance can be used to help track down their sources and distributionchannels. The system provides the ability to detect factory overruns oflabels or products, monitor the number of labels produced, and so on.

It is to be understood that even though various embodiments andadvantages of the present invention have been set forth in the foregoingdescription, the above disclosure is illustrative only, and changes maybe made in detail, and yet remain within the broad principles of theinvention. For example, many of the components described above may beimplemented using either digital or analog circuitry, or a combinationof both, and also, where appropriate, may be realized trough softwareexecuting on suitable processing circuitry. Therefore, the presentinvention is to be limited only by the appended claims.

1-13. (canceled)
 14. A security device comprising an arrangement oflight-emitting particles on a surface, said arrangement forming apattern of varying spectral emission properties corresponding to each ofthe light emitting particles.
 15. The security device of claim 14,wherein said light-emitting particles are selected from the groupconsisting of fluorophores, quantum dots, fluorescent fibers, andnanometer-sized particles.
 16. The security device of claim 14, whereinsaid light-emitting particles are quantum dots composed of a pluralityof layers including at least one layer of a semiconductor material. 17.The security device of claim 16, wherein said semiconductor material iscomprised of a first layer of CdSe and a second layer of ZnSe.
 18. Thesecurity device of claim 14, wherein said arrangement provides arepresentation of information that is at lest one of random andstructured information. 19-20. (canceled)